Display tech to watch this year: OLED's future looks bright

The thin, bright, energy-efficient displays may outclass LCD and plasma TVs -- if manufacturers can scale up.

Computerworld |

Editor's note: This is the conclusion to our four-part series on display technologies to watch in 2011.

If the screen on that sleek smartphone you just bought looks unusually bright and colorful, you might not be looking at an LCD at all. The displays in models such as the Samsung Galaxy S, the Google Nexus S and the HTC Droid Incredible rely on active-matrix organic light-emitting diodes (OLEDs), an alternative display technology that's faster, thinner and lighter, offers more vivid colors at higher contrast, and uses as little as one quarter of the power consumed by your typical backlit, active-matrix LCD.

OLEDs have been around for more than a decade but have taken off only within last few years, and only for very small screens. Over 40 million active-matrix OLED phones shipped in 2010, and volumes will continue to increase this year, according to market research firm DisplaySearch.

Now the technology is getting ready to bust out of the mobile phone market and make its way into tablets, TVs and more -- provided manufacturers can reduce production costs for OLED displays, which are now significantly higher than for LCDs.

And OLEDs have another cool attribute: The display media can be constructed on a flexible substrate, such as plastic or bendable foil, rather than the breakable, rigid glass backing used in LCDs. That sets the stage for a new generation of even lighter and more rugged displays in the next few years -- and for curved, flexible, and even rollable displays down the road.

Note: For greater readability, we've shortened AMOLED (active-matrix OLED) to OLED throughout this story. Passive-matrix OLED (PMOLED) displays are not used in smart computing devices or high-performance screens.

Fast, bright and energy efficient

Today's commercially available active-matrix OLED displays are built on a version of the same electrical foundation as LCDs -- an active-matrix thin film transistor (TFT) array fabricated on glass, which drives the display media above it (see "The display sandwich").

But the layers of organic material that make up the OLED display media emit red, green and blue light, so no backlight is required, and the light doesn't have to pass through color filters, as it does with LCDs. That's what gives an OLED display its brilliance and energy-efficiency edge. (Story continues on next page)

The display sandwich

A flat display is a complicated sandwich of materials, says Nicholas Colaneri, director of the Flexible Display Center at Arizona State University. Take an LCD, for example. At the bottom is a substrate, usually glass, upon which manufacturers fabricate a layer of thin film transistors out of silicon. The transistors in the TFT layer power the liquid crystal display media layer above it.

The TFT layer activates the liquid crystal layer, "which acts like a venetian blind," Colaneri says. A backlight mounted behind the display sends light up through the liquid crystal and then through a color filter layer to produce the red, green and blue pixels that create the final image.

This display stack shows UDC's phosphorescent OLED technology, but the layers are basically the same for all active-matrix OLEDs. Source: UDC.

With an active-matrix OLED, manufacturers replace the liquid crystal and color filters with a series of four to seven layers of organic films sandwiched between two metal contacts. The films, mere thousandths of an angstrom thick, are a fraction of the size of the liquid crystals in an LCD.

The TFT layer applies the voltage to power the OLED layers. "When you push current through that stack, light comes out of it," says Colaneri. So while the OLED stack still needs a TFT layer to make it work, the display sandwich can dispense with the backlight and color filter layers.

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